Ind ian Journal or Chcmistry VoI.4SA. Junc2006,pp. 13SG- 13G I

Unusual coordination preferences of flexible tetradentate ligands and thiocyanate anions leads to trailS nickel(TI) and cis manganese(II) compounds Tar ~t1 1 K Karmakar", Barindra K Ghos h" , A Usmanb

, Hoong- Kun Fun!> & Swapan K Chandra"·e.*

"Departmcnt or Chemistry . The Uni versity or Burd wan, Burdwan 713 104, India Email : dr_swapan @siry.com

hX-ray Crysta ll ograph y Unit. Schoo l of Phys ics, Uni vers iti Sai ns Malaysia, 11 800 US M. Pcnang. Malaysia <Dcpartmcnt ofChcmistry, Vi sva-B harati Univcrsity. Santi niketan 73 1 23S , India

Rece i ved 30 Nov('/Ilber 2005; revised 24 February 2006

The synthes is, characteri sa ti on and propertics or two tmlls nickel(lI ) complcxes with thiocyanate coordin ation. [Ni(L I )(NCS)lJ (1) :1 nd I Ni(L2)(NCS)ll (2) and compari son or thc results with cis- IMn(L 1)( CS h l (3) and cis-IMn(L2)(NCSh] (4) (L I and L2 = tctradcntak ligands. dcrived from bi s condensat ion bctwecn pyrid inc-2-carboxaldehyde and 1.3-diaminopropanc and 2-bcnzoyl pyridine and 1.3-diaminopropane respccti vcly) arc dcscribcd. Thc stru ctures have been detcrmincd by si ngle crystal X-ray dilTraction slUdi es. Study reve:tl s til at the nickcl atom always produces t/'{fIlS isomer and mangancsc atom givC's the CIS isomer. Both metals arc hcxacoordinatcd with an unu sual prei'cren ti al binding or tet radclllate liga nds and thi ocyanatc anions.

IPe Code: In l.. CI. K C07F 13/00; C07F IS/04

In the last couple of decades there has been rapid advancement in the fi eld of coordinat ion chemi stry of nickel and manganese with numerous li gands due to their signifi can t role as redox active site in several biochemical processesl-I.J, the diversity of their magneti c properti es l5-25 and building bloc ks of supramolec ul ar architecture through variety of non­cova lent intermolecu lar interac ti ons26. Designing suitab le polydentate li gands leading to a number of transiti on metal coordinati on compounds fo r their powerful stabili zing potenti al has gained some importance l .J.26.27. Pseudohalide ani ons (N)-. NCS-, NCO-) have been well documen ted for their ve rsati le coordi nation abi Ii ti es leadi ng to vari ety of species 19.20.

Herein we report the unusual preferential coodinati on behaviour of tetradentate li gand systems (L1 and L2) and thi ocyanate anions whi ch produces lralls ni ckel(II ) complexes INi (Ll )( CS)2] (1) and I Ni(L2)(NCS h] (2) (Ll and L2 = tetradentate li gands. deri ved from bis condensati on between pyrielin e-:~ ­

carboxa ldehyde and LI-diaminoprorane and 2-benzoyl pyridine and J .3-diaminopropane respective ly) We have previously obse rved that these two I iga nds and thiocyanate anion coorel i na ted to manganese(lI) always ge nerates tile cis isomcrs

""5 IMn(Ll)(NCSh J (3) and IMn(L2)(NCS)21 (4f . The synthesis. characteri sation i ncl ud i ng X-ray Slruct ure and magneti c propcrties or these new compounds arc described herein.

Materials and Methods 1 J-Diami nopropa ne, pyridi ne-2-carboxaldehyde.

2-benzoyl pyridine and ammonium thi ocyanate were purchased from Lancaster Chemical Company Inc. and used as received. All other solvents and chemi ca ls were of analytical grade. The tetradentate li gands (Ll and L2) were synthesized adopting a procedure as reported previously and gave sa ti sfactory elemental

I . 23

ana YS tS . Elemental analyses for carbon, hydrogen and

nitrogen were performed (a t lACS. Kolkata) using a Perkin-Elmer 2400II elemental analyzer. Manganese contents were determined by titrimetri c I ethod. IR spectra (4000-400 cm- I) were recorded on (K8 r pellets) at 298 K uSIng a JASCO FfIlR-420 spectrometer. Magneti c suscepti bi Ii ti es were measured at 298 K using a magnetometer (Sherwood Scienti fico model MKl ). Pasca l' s constanrs were utili zed to es timate diamagneti c correction and th is va lu ,vas subtrac ted from the experimenta l suscepti bi lity data to gi ve molar magnetic susceptibility (X:v1 ). Solu tion (ca. 10-' mol dm-')

f:!, / H

H ..... / c ........ c/ H H,A( ..... H

Ft.. I 1 ~ ©tC=N N=C'© L1 w!lenR=H L2 when R = Ph

KARMAKAR ef al.: UNUSUAL THIOCYANATE COORDINATION IN Ni (lI ) & Mn(lI) COMPLEXES 1357

electrical conductivities were measured with a Philips PR 9500 bridge.

Prcpamtion of trails [Ni(Ll)(NCSh], (1)

An acetontrile solution (8 cm3) of the ligand Ll

(0.063 g, 0.25 mmol) was added dropwise to an acetontri le solution (10 cm3

) of Ni(CI04h.6H20 (0.091 g, 0.25 mmol) with constant stirring for 0.5 h at room temperature. To the resulting yellowish­brown coloured solution , an aqueous acetonitrile solution (0.5 cm3 water + 2.5 cm3 acetonitrile) of ammonium thiocyanate (0.038 g, 0.5 mmol) was added d [, ) wise. The brown solution was then left for slow evaporation and after 3 days, a brown-red crystalline compound (1) suitable for X-ray analysis was obtained. Yield: 0.080 g, 75 % (Anal. : Found: C, 47 .9; H, 3.7; N, 19.7; Ni , 13.5. Calcd. for CI7HI6N6S2Ni : C, 48 .0; H, 3.8; N, 19.7, Ni , 13 .7%). IR data: 2080, 1635, 1584 cm- I.

PI-cparation of trails [Ni (L2)(NCSh], ( 2)

A methanolic solution (6 cm3) of the ligand Ll

(0.063 g, 0.25 mmol) was added dropwise to a methanolic solution (6 cm3

) of Ni(N03h.6H20 (0.073 g, 0.25 mmol) with constant stirring for 0.5 h at room temperature. To the resulting light green colour solution a methanolic solution (6 cm3

) of ammonium thiocyanate (0.038 g, 0.5 mmol) was added slowly. The greenish brown solution was then left for slow evaporation and after 3 days, brown crystalline compound (2) suitable for X-ray analysis was obtained. Yield: 0.105 g, 73% (Anal.: Found: C, 60.0; H, 4.1; N, 14.6; Ni , 10.2. Calcd. for C29H24N6S2Ni: C, 60.1; H, 4.2; N, 14.5, Ni, 10.1 %). IR data: 2074, 1639, 1589cm-l

.

Preparation of cis [Mn(Ll)(NCS)z], 3 and cis [Mn(L2)(NCSh], 4

These two compounds were synthesized following a procedure as reported previously and gave satisfactory elemental analy~is28.

CAUTION: Perchlorate salts complexes are potentially explosive especially in presence of organic ligands. These complexes must be prepared and handled in small quantities, and with special care.

Crystal structure

Single crystals suitable for X-ray crystallographic analysis were selected in all cases following examination under a microscope. Single crystal X-ray diffraction data for all compounds were col lected on a Siemens SMART CCD diffractometer fitted with graphite monochromator with Mo-Ka radiation

(A = 0.71073 A) at 213(2)° K with a detector distance of 4 cm and a swing angle of -35°. A hemisphere of reciprocal space was covered by a combination of three sets of exposures (each set had a different <!>

angle (0, 88, 180°) and each exposure of 30 s covered 0.3° in w). Data collection, indexing and initial cell refinement were handled using SMART software29. Frame integration and final cell refinement were carried out using SAINT software30

. The SADABS software package31 was used to perform the absorption corrections. The atomic scattering factors are from the International Tables for Crystallography. The structure was solved by d:rect methods, completed by subsequent difference Fourier syntheses and refined by full-matrix least-squares procedures on F2 using SHELXTe2. The non hydrogen atoms were refined anisotropically. The hydrogen atoms were refined with geometrical constraints with ideal bond lengths and angles and were treated as riding atoms. All computations were carried out on a PC using the SHELXTL-PC program package. The figures were made using ORTEP-3 program packages33

. The crystal data and data collection detai Is are collected in Table 1.

Results and Discussion The reaction of ligand Ll or L2 with nickel(II) and

manganese(II) nitrate/perchlorate hexahydrate and ammonium thiocyanate using a ratio of Ll or L2: NilllMn li

: NCS- = 1 : 1 : 2 in aqueous methanol or aqueous acetonitrile medium afforded respectively brown-red trans-[Ni(Ll)(NCSh] (1), greenish-brown trans-[Ni(L2)(NCSh] (2), yellowish green cis­[Mn(Ll)(NCS)2] (3) and orange cis-[Mn(L2)(NCSh ] (4) crystalline compounds. It is interesting to note that changing the ratio of Ll or L2 : Ni ll / Mn ll : NCS- = 1 : 1 : 1 to any other ratio to make different thiocyanate bridged bi- or polynuclear compounds led to the same compounds 1, 2, 3 and 4 respectively. In DMF and acetonitrile, these compounds behave as non­electrolyte34

, as indicated by their very low AM values (5-7 Q-I cm2 mor l

). The magnetic moments in polycrystalline form are 2.91 (for compound 1), 2.82 (for compound 2), 5.95 (for compound 3) and 5.86 (for compound 4) BM at 298 K, corresponding to idealised t2/e/, S = 1 for nickel(II) compounds and a high-spin idealised t2/e/, S = 5/2 electronic configuration with five unpaired electrons as expected for manganese(II) species IS. The X-band EPR spectra of the manganese chelates 3 and 4 were examined in

1358 INDIA N J C HEM , SEC A, J UNE 2006

Table I - The crystal data and data co llec tion summary for trailS [Ni (L 1)( CSh] 1 and t ra il s [Ni (L2)(NCS h ]2

Empi ri cal formu la C I7H 16N6S2Ni C29H24N6S2Ni

Formula weight 427 . 19 579.37

Space group P2 1/c (no. 14) P2 1/n (no. 14)

a (A) 8. 1783( 1) 9.4898(2)

b (A) 9.438 I ( I) I 1.340 I (2)

c (A) 24 .7003(2) 26.3325( I)

a (0) 90 90

~ (0) 98.741( 1) 92 . 176( 1)

Y (0) 90 90

V(p) 1884.4 I (3) 283 1.74(8)

Z 4 4

P ... lcd (g CIll ·3

) 1.506 1.359

F(OOO ) 880 1200

Crystal size (mm) 0.36x 0. 18 x 0.16 0.40 x 0.26 x O. I 2

~ (Mo Ka) (mm· l) 1.264 0.862

Ic(A) 0.71073 0.71073

Temp. (K) 183 183

20m., (0) 56.0 54.0

Reflections collected 13034 18389

Independent 4499 (Rilll = 0.096) 6 1 18 (Rilll = 0.098) retlections

Reflect ions observed 4499 6 118 [I > 2.0cr(l)]

Goodness-or-fit 1.01 0.889

R'; wR b 0.0460; O. I 055 0 .0488; 0.1013

Largest di fference 1.29 and - 1.20 0 .447 and - I .021 peak and hole (e k 3

)

aR =L ( I I Fo I-I Fe II )/L I Fo l ; bwR = {LW( I Fo 12_ I Fe 12)2/Lw CFo 2)2} 1/1

1: 1 DMF-toluene glass (77 K). The spectra of the two complexes were similar. In the magnetically dilute glassy state, the 55Mn hyperfine structures were observed at g = 2 with peak-to-peak separation of about 85 G. The nicke l(II) complexes were EPR silent as expected.

The ill spectra of 1, 2, 3 and 4 exhibit a very strong absorption at 2080, 2074, 2063 and 2071 cm· l

respectively that corresponds to the asymmetric stretching vibrations of N bonded thicyanate35. The absorptions corresponding to the v(C=N) stretches of Ll and L2 are located around 1630 and 1580 cm-l for all compounds2 1,35 .

C14

~C6

C9

C8

Fig. I - ORTEP plot with atom numberi ng scheme for trans-[Ni (Ll)(NCShl (I ). For c larity the hydrogen atoms

are not shown.

C10 C9 N2

C1~~ N3

C~ '

C15 C16

N5

.~ -~1

Fig. 2 - ORTEP plot with atom numbering scheme for cis-[Mn(Ll )(NCS)2] (3). For c larity the hydrogen atoms

are not shown.

Crystal structures of trans-[Ni(Ll)(NCSh], ( I) , trans-[Ni(L2)(NCShJ, (2), cis-[Mn(Ll)(NCS)2], (3) and cis-[Mn(L2)(NCShl, (4)

The ORTEP drawing of the complexes trans­[Ni(Ll)(NCS)2] (1), cis-[Mn(Ll )(NCSh] (3) , trans­[Ni(L2)(NCSh ] (2) and cis-[Mn(L2)(NCSh] (4) are shown respectively in Figs 1 ~4 , and the selected comparison of bond distances and angles are listed in Tables 2 and 3. Both nickel(II) and manganese(II) are located in a highly distorted octahedral (MnN6) coordination environment consisting of two nitrogen atoms (Nl and N2) from the N bonded thiocyanate anion and four nitrogen atoms (N3 to N6) from the

KARMAKAR e/ al.: UNUSUAL THIOCYANATE COORDI NATION I Ni(l l ) & Mn(ll ) COMPLEXES 1359

C2

Fig. 3 - ORTEP plot with atom numbering scheme for /ralls-[Ni (L2)(NCS)21 (2). For clarit y the hydrogen atoms

are not shown.

Table 2 - Selected bond distances (A) and bond angles (0) in /ram-[Ni(L I )(NCS)21 (1) and cis-[Mn(L I )(NCS)2] (3)

BOlld dis/all ces /ram [Ni (L I )(NCS)zl (1) cis- Mn(L I )(NCS)21 (3)

M-N( I ) 2. I 32(2) 2.3495( I 3)

M-N(2) 2.063(2) 2.255 1( 13)

M-N(3) 2.066(2) 2.3078( I 3)

M-N(4) 2.145(2) 2.27 12( 13)

M-N(5) 2.06 1 (2) 2. I 752( 14)

M- (6) 2.056(2) 2.1734( 14)

BOlld allg les //'{III S [N i(L I )(NCS)21 (1) cis-Mn(L I )(NCShl (3)

N( I )-M-N(2) 79.23(8) 7 I .20(5)

N( I )-M-N(3) 171.97(8) 120.80(5)

N( I )-M-N(4) 109.47(8) 94.63(4)

(2)-M-N(3) 92.86(9) 78.86(5)

N(2)-M-N(4) 17 I .25(8) 134.42(5)

N(3)-M-N(4) 78.47(8) 7 1.94(4)

(S)-M-N(6) 176.18(9) 86.72(5)

tctradentate li gand . It is to be noted that in the case of manganese, the di stortion of angles in the coordination sphere is so acute that it is very difficu lt to ascertain whether the angle has deviated from cis or lrans position. But inte restingly, the thi ocyanate anions are very close to cis (average ang le is 88 .98(7)°) in the case of manganese, and trails (average ang le is 176.54(11 )°) in the case of nickel. The Mn-N di stances are always larger in case of manganese than that of corresponding Ni-N di stances.

C12 C 11

~~ C10 ~ ~ C9

C13 'Q:""'12:

C5 C6 ..Q if "~C4

C 7l b C3 81

~7 C1./: ~ MnN4 C29

_.~j N6 C28

C1 7 ~f' h~V C20 C1 ~ C7.IJ C27

C21 ~ C22~

C23

C14

Fig. 4 - ORTEP plot with atom numbering scheme for cis- [Mn(L2)(NCS)21 (4). For clarity the hydrogen atoms

are not shown.

Tab le 3 - Selected bond distances (A) and bond angl es (0) in /rall s- [N i(L2)(NCS)21 (2) and cis- [Mn(L2)(NCS)21 (4)

BOlld dis/an ces /rall s- [Ni (L2)(NCSh l (2) cis-[ Mn(L2)(NCS)21 (4)

M-N( I ) 2. 122(2) 2.358 1( 18)

M-N(2) 2.037(2) 2.2420( I 8)

M-N(3) 2.081 (2) 2.3670( 19)

M-N(4) 2.080(2) 2.2757( I 8)

M-N(S) 2.079(3) 2.172(2)

M-N(6) 2.062(3) 2. 184(2)

Bond ang les /ralls- [Ni (L2)(NCSh l (2) cis-[Mn(L2)( CSh] (4)

N( I )-M-N (2) 78.68( I 0) 7 1.30(6)

N( I ) -M-N(3) 17 1.92(9) 10982(6)

N( I )-M-N(4) 107.77( 10) 9S .60(6)

N(2)-M-N(3) 9492( I 0) 8100(6)

N(2)-M-N(4) I 72.60( I 0) 143. 1 4~6 )

N(3)-M-N(4) 78.9S( 10) 7 114(6)

N(S)-M-N (6) 176.90( 11 ) 9 1.24(7)

The average di stance of the Mn-N(NCS) bond is 2. 176(2), wh ile that of Ni -N(NCS) is 2.065(3) A. The average distance of Mn-N(Ligand) is 2.3046(19),

1360 INDIAN J CHEM, SEC A, JUNE 2006

wh ile tll~ l t of Ni-N(Ligand) average distance is 2.091(3) A. The M-N(thiocyanate) distances are considerably shorter than M-N(ligand) distances as expected due to stronger binding capabi lity of th iocyanate anion as compared to that of neutral polydentate ligand36. All these M-N distances are consistent with correspondi ng values of the analogous MnN6 chromophores36-38

. The most possible origin of this substantial deformation of these compounds may be the structural constraints imposed by the polydentate ligand backbone. This type of unusual preferential binding of polydentate ligand and thiocyanate anions leading to cis isomer in manganese and tran s isomer in nickel as well as distortions in the coordination sphere (especially for manganese) has not been observed even in topologically constrained pentadentate37 or other constrained macrocyclic ligand systems39

. We have observed this type of severe distortion in the case of manganese using pentadentate ligand system and thiocyanate anion as terminal donor36. The possible reason of obtaining cis and trans isomers in the case of manganese(II) and nickel(IT) respectively may be linked to larger ionic radii of mangane(II) as compared to nickel(II) (for high-spin manganese(II) : 0.97 A and nickel(Il) : 0.83 A). Another reason may be the structural constraint imposed by the rigid ligand framework, which has also been reported recently by other workers36

.37.4 1. Due to the large size of manganese, coordination sphere is highly distorted and M-N distances are larger as compared to corresponding distances of nickel (vide supra).

The above study describes the unusual preferential ligation of tetradentate li gands showing that the thiocyanate anions leads to always the cis isomer in the case of manganese(II) and lrans in the case of nickel(II). All four complexes have distorted coordination spheres around the metal and in the case of manganese, this distortions is acute. This type of observations and thereby stability using linear tetradentate ligand is reported for the first time here. The studied ligand, therefore, shows the possibility of ,preferential coordination behaviour to produce different isomers for nickel(II) and manganese(II) compounds.

Supplementary Material Crystallographic data for the structural analysis

have been deposited with the Cambridge Crysta ll ographic Data Centre, CCDC No. 288843 and 288844 for compounds 1 and 2 respectively and

previously deposited CCDC No. 259337 and 259338 for compounds 3 and 4 respectively .. Copies of thi s information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 lEZ, UK (Fax: 44-1223-336033; Email : deposit @ccdc.cam.ac.uk or www:http://www.ccdc.cam. ac.uk) .

Acknowledgements This work was supported by grants from the

Department of Science and Technology (Grant No. SRIS IIIC-22/2003, S.K.c.) and Counci l of Scientific and Industrial Research (Grant No. 01(l836)/03/EMR-ll, S.K.c.), New Delhi. T.K.K. thanks University Grants Commission, New Delhi , for a teacher fellowship. H.K.F thanks the Malaysian Government and Universiti Sains Malaysia for research grant R&D No. 305/PFIZIKl610961.

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